Endoscopes of this type are generally known in the art. The inner tube of the shaft serves for the insertion of optical components such as rod lenses. Between the inner tube of the shaft and the outer tube that surrounds the inner tube, it is customary to configure an open ring of space that serves, for instance, to contain optical fibers in order to conduct light to the distal end of the endoscope and thus to the surgical area that is to be investigated.
The endoscopes must be sterilized after each use, and for this purpose they are subjected in autoclaves to damp heat in the temperature range of 120 to 140 degrees C. Because of the different materials of the two tubes of the instrument shaft in connection with temperature fluctuations and/or because of temperature differences between the outer and inner tube, as a result of a delay in conducting heat from the outer tube to the inner tube, the outer tube and inner tube expand at different rates from the impact of these sometimes extreme temperatures. To allow a reduction of the resulting tensions between the tubes of the instrument shaft joined together on the distal end, the outer and inner tubes are mounted on the instrument housing so that they can move in relation to one another in the axial direction of the shaft.
A generic endoscope with length compensation at thermal impacts is known for instance from DE 197 13 275 A1. With this known structure the outer and inner tubes of the shaft forming one component insulated against fluids are each connected on the proximal end with a separate housing part of the instrument housing. To make possible the required axial relative movement between the outer and inner tubes, the two separate housing parts are floating mounted on one another by means of O-rings inserted between them.
This known construction has fully proven itself and allows a sufficient thermal length compensation of the shaft tubes, but the O-rings in particular at high thermal pressure during the cleaning of the endoscope do not ensure any permanent fluid-tight insulation of the instrument housing.